Lighting systems and display systems, such as projection systems, are used for various applications such as for example for displaying images, in watches, in calculators, in computerised systems, in simulation systems and for projecting information or images onto a distant screen. Most projection systems basically comprise a lamp for generating light, illumination optics for capturing that light and transferring it to one or a plurality of light modulators and a projection lens which images the illuminated light modulator on a screen.
Light emitting diode (LED) devices are being increasingly used in projection and lighting applications. They have advantages of a long operational life, low operating power and low emitted heat. A disadvantage of LED devices is that an individual device emits a relatively low level of light. For an efficient projector system comprising such an illumination source it therefore is important to transfer the light from the illumination source as efficiently as possible in the light path. Nevertheless, collecting light is substantially impeded by the typical packaging constraints of typical light sources such as e.g. a light emitting diodes.
In order to fulfil the high brightness requirements for many of today's applications, it is desirable to use multiple light sources, such as LED devices in order to obtain increased light output. The packaging constraints of individual light sources nevertheless pose a problem for efficiently gathering light emitted by multiple devices. In particular, the packaging of individual devices makes it is difficult to locate multiple devices closely together.